Iron(I) hydride, systematically named iron hydride and poly(hydridoiron) is a solid inorganic compound with the chemical formula (FeH)n (also written ([FeH])n or FeH). It is both thermodynamically and kinetically unstable toward decomposition at ambient temperature, and as such, little is known about its bulk properties. Iron(I) hydride is the simplest polymeric iron hydride. Due to its instability, it has no practical industrial uses. However, in metallurgical chemistry, iron(I) hydride is fundamental to certain forms of iron-hydrogen alloys.